No doubt that there are some people with OS X servers who'd like to use ownCloud. And as you can see in the github-discussion there were quite some efforts to run it on these platforms, even when there was no official OS X support any more: https://github.com/owncloud/core/issues/2377
It probably would require some time and knowledge on OS X systems to make it work which ownCloud can't provide. But people can contribute to ownCloud and implement OS X support (or pay someone to do so).
As a workaround you can use virtual machines to run Linux, or use Linux or *BSD directly on Mac hardware (some seem to be supported).